This invention relates to an image formation apparatus comprising: image formation means for forming color-component images corresponding to a plurality of color components onto a plurality of image-carrying bodies respectively that correspond to the respective color components; and a transfer medium onto which the respective color components formed on the image-carrying bodies are transferred; and adjusts the timing for forming an image based on the positions of the respective color-component images that are transferred to the transfer medium.
There are image formation apparatuses for forming color images on paper that form color-component images onto respective photosensitive drums for black, cyan, magenta and yellow, for example, and then transfer and overlay the images onto a transfer belt. Formation of the color-component images onto each of the respective photosensitive drums is performed by using a plurality of polygon mirrors that correspond to the respective photosensitive drums to reflect laser beams that are outputted from a plurality of laser diodes that correspond to the respective photosensitive drums, and irradiate the respective beams onto the respective photosensitive drums. There are also apparatuses in which the number of polygon mirrors is reduced, and irradiate laser beams from a plurality of laser diodes onto a common polygon mirror, and irradiate the respective laser beams reflected by the polygon mirror onto the respective corresponding photosensitive drums.
In these kinds of image formation apparatuses, there is a problem in that there is a decrease in image quality due to position shift of the color-component images that are transferred to the transfer belt. Therefore, images (hereafter referred to as a marks) are formed for adjusting the image formation timing, and the position of the formed marks is detected and image formation timing is adjusted based on the detected position of the marks (for example, refer to Japanese Patent Application Laid-Open No. 4-149478 (1992)).